This invention relates to fluorescent compounds. In one aspect it relates to fluorescent compounds that have been synthesized and undergone stability testing for use as inert tracers in industrial water systems. In another aspect of this invention there are provided alternative processes for the production of fluorescent compounds.
Using an inert fluorescent compound to track the hydraulic losses and gains from an industrial water system has been known since the late 1980""s.
Industrial water systems are very numerous. One typical industrial water system is a cooling tower where water is used in a heat exchange role. To optimize use of treating agents in such systems and to assure overall appropriate hydraulic conditions are maintained in the system, it is advantageous to determine the amount of treating agent added to the system in accordance with recommended use levels specific to the environment. If there is an under treatment of treating agent, deposition of scaling salts and corrosion may rapidly occur. If there is an over treatment of treating agent, treating agent will be wasted with a commensurate loss of money.
The continuous on-stream monitoring of the amount of a treating agent added to a moving body of water through the use of a tracer comprising an inert fluorescent compound is an established practice as described in U.S. Pat. Nos. 4,783,314 and 4,992,380. These patents contain background information which need not be repeated here but the contents of which are incorporated herein by reference.
To be useful in such systems, the fluorescent compound employed must be non-consumable or system-inert. There are certain known compounds that are capable of functioning as inert fluorescent tracers, however, there are not an abundance of such compounds. Therefore, there is a continuous need for the development of additional inert fluorescent tracer compounds that are capable of functioning in aqueous systems, particularly where such systems contain oxidizing biocides.
The first aspect of the instant claimed invention is a fluorescent compound of the formula: 
wherein R1 and R2 are either both SO3M, or one of R1 and R2 is SO3M and the other is COOM, where M is selected from the group consisting of H, Na, K, Rb, Cs, Li or ammonium.
The second aspect of the instant claimed invention is a process for the preparation of a fluorescent compound having the formula: 
wherein R1 and R2 are as defined previously, which comprises condensing a 1,8-naphthalic anhydride of the formula: 
with an o-phenylene diamine of the formula: 
where R1 and R2 are as defined previously.
The third aspect of the instant claimed invention is a process to make fluorescent compounds of formula I: 
by condensing o-amino-nitro aromatics of the formula 
where R1 is as defined previously, with the appropriate 1,8-naphthalic anhydride: 
where R2 is as defined previously,
wherein such condensation is carried out in such a manner that in situ reduction of the nitro group is accomplished with a suitable reducing agent.
The fourth aspect of the instant claimed invention is the use of a compound of formula: 
where R1 and R2 are as defined previously, as an inert fluorescent tracer in an industrial water system.
This invention is based upon the discovery of certain naphthalimide-based compounds. These naphthalimide-based compounds are not only fluorescent, but are also stable in the presence of oxidizing biocides such as bleach, bromine, stabilized chlorine and stabilized bromine. Therefore, these certain naphthalimide-based compounds are particularly useful as inert fluorescent tracers in industrial water systems containing bleach and/or stabilized bromine.
These certain naphthalimide-based compounds can be readily prepared through the condensation between a 1,8-naphthalic anhydride possessing the appropriate functionalities with the appropriately substituted o-phenylene diamine. They can also be prepared by the condensation of a 1,8-naphthalic anhydride possessing the appropriate functionalities with an o-amino-nitro aromatic in the presence of a suitable reducing agent.
The fluorescent compounds of the present invention are naphthalimide-based compounds of the following structure: 
wherein R1 and R2 are either both SO3M, or one of R1 and R2 is SO3M and the other is COOM, where M is selected from the group consisting of H, Na, K, Rb, Cs, Li or ammonium.
The fluorescent compounds of the present invention can be conveniently prepared by a one-step condensation between a 1,8-naphthalic anhydride possessing the desired functionalities and the appropriately substituted o-phenylene diamine. Suitable 1,8-naphthalic anhydrides for preparing the fluorescent compounds in accordance with the present invention are ones selected from the group of the formula: 
wherein R2 is as defined previously. When R2 is SO3K, then Compound II is 4-sulfo-1,8-naphthalic anhydride, potassium salt and Compound II is available from Aldrich Chemical Company, P.O. Box 2060, Milwaukee, Wis. 53201 USA; Telephone Numbers (414) 273-3850 and (800) 558-9160.
Similarly suitable o-phenylene diamine compounds which are useful in the preparation of the fluorescent compounds of the present invention are ones of the formula: 
wherein R1 is as defined previously. When R1 is COOH, then Compound III is 3,4-diaminobenzoic acid and Compound III is available from Aldrich. When R1 is SO3H, then Compound III is 3,4-diaminobenzene sulfonic acid and Compound III is available from Bayer AG, Organic Chemicals Business Group, Marketing, Leverkusen, D-51368, Germany, Telephone Number +49 214 30-8514.
In a presently preferred embodiment of this invention, the fluorescent compounds can be prepared in a one-step condensation between an appropriately substituted naphthalic anhydride and an appropriately substituted o-phenylene diamine.
Alternatively, o-amino-nitro aromatics of the formula 
where R1 is as defined previously, can be condensed with the appropriate 1,8-naphthalic anhydride when such condensation is carried out in such a manner that in situ reduction of the nitro group is accomplished with a suitable reducing agent such as, but not limited to, iron powder. When R1 is SO3M then compound IV is o-nitroaniline-p-sulfonic acid (and salts thereof) and Compound IV is available from Bayer AG. When R1 is CO OH, then Compound IV is 4-amino-3-nitro benzoic acid, and Compound IV is available from ACROS Organics, which is part of Fisher Scientific, 600 Business Center Drive, Pittsburgh Pa. 15205, telephone number 1-800-227-6701. When R1 is SO3M then Compound IV is 2-nitroaniline-4-sulfonic acid and its salts, and Compound IV is available from TCI America, 9211 North Harborgate Street, Portland Oreg. 97203, telephone number 800-423-8616.
Fluorescence is defined as the reemission of longer wavelength (lower frequency) photons (energy) by a molecule that has absorbed photons (light) of shorter wavelengths (higher frequency). Both absorption and radiation (emission) of energy are unique characteristics of a particular molecule (structure) during the fluorescence process. Light is absorbed by molecules causing electrons to become excited to a higher electronic state. The electrons remain in the excited state for about 10xe2x88x928 second then, assuming all of the excess energy is not lost by collisions with other molecules, the electron returns to the ground state. Energy is emitted during the electrons"" return to their ground state. The Stokes"" shift is the difference in wavelength between absorbed and emitted light. The emitted wavelength is always longer or equal to the incident wavelength, due to energy conservation; the difference is absorbed as heat in the atomic lattice of the material.
When their fluorescent properties were tested, it was found that the instant claimed compounds have a fluorescent signal excitation value above 380 nm. Thus, these compounds have a different fluorescent signal than Nalco Chemical Company""s inert tracer 1,3,6,8-pyrene tetrasulfonic acid tetrasodium salt (PTSA). PTSA is available from Nalco Chemical Company, One Nalco Center, Naperville, Ill. 60563, telephone number (630) 305-1000. Thus, the instant claimed tracers can be used together with PTSA for monitoring and control purposes in an industrial water system, because their fluorescent signal does not overlap with that of PTSA.
The inert fluorescent compounds of this invention exhibit excitation and emission maxima in the range of 385-400 nm and 510-530 nm respectively. This broad spectral operating range, afforded by the compounds of the present invention, will enhance the utility of these compounds as inert fluorescent tracers. In addition, the large difference between the excitation and emission maxima (called the Stokes shift) may serve to minimize interference due to background hydrocarbons, since very few species have a Stokes shift this large.
The fluorescent compounds of this invention can be used in any industrial water system where an inert fluorescent tracer is needed. Examples of such systems are cooling tower water systems (including open recirculating, closed and once-through systems); petroleum wells, downhole formations, geothermal wells and other oil field applications; boilers and boiler water systems; mineral process waters including mineral washing, flotation and benefaction; paper mill digesters, washers, bleach plants and white water systems; black liquor evaporators in the pulp industry; gas scrubbers and air washers; continuous casting processes in the metallurgical industry; air conditioning and refrigeration systems; industrial and petroleum process water; indirect contact cooling and heating water, such as pasteurization water; water reclamation and purification systems; membrane filtration water systems; food processing streams (meat, vegetable, sugar beets, sugar cane, grain, poultry, fruit and soybean); and waste treatment systems as well as in clarifiers, liquid-solid applications, municipal sewage treatment and industrial or municipal water systems.
When using the fluorescent compounds of this invention as inert tracers in industrial water systems, it is generally desirable to employ the least amount of fluorescent compound that is practical for the circumstances. It is, of course, understood that the amount of the fluorescent compound added to the water system has to be at least an amount sufficient for the fluorescent signal measurements to be made. Generally, the system concentration of an insert fluorescent compound at the sampling site in the water system should be at least about 0.01 ppb and not more than about 10 ppm. Preferably the concentration of fluorescent compound is between about 50 ppb and about 500 ppb. Most preferably the concentration of fluorescent compound is between about 100 ppb and 400 ppb. Of course, it is possible to add more than 10 ppm of the inert fluorescent compound to the water system and detect the fluorescent signal of the compound, but the use of any amount of inert fluorescent compound over 10 ppm is an unnecessary waste of inert fluorescent compound.
The meaning of the term xe2x80x9cinertxe2x80x9d, as used herein is that an inert fluorescent tracer is not appreciably or significantly affected by any other chemistry in the system, or by the other system parameters such as metallurgical composition, microbiological activity, biocide concentration, heat changes or overall heat content. To quantify what is meant by xe2x80x9cnot appreciably or significantly affectedxe2x80x9d, this statement means that an inert fluorescent compound has no more than a 10% change in its fluorescent signal, under conditions normally encountered in industrial water systems. Conditions normally encountered in industrial water systems are known to people of ordinary skill in the art of industrial water systems.
Of course it is possible to cause more than a 10% change in the fluorescent signal by subjecting the fluorescent compound to stress that is not normal for an industrial water system. For example, the fluorescent signal of one of the instant claimed compounds (disulphonaphthalimide or DSN) will change more than 10% if the compound encounters more than 42000 ppm of pyrophosphate (as PO4), or if it encounters more than 34000 ppm of sodium (as Na+). The fluorescent signal of another one of the instant claimed compounds (carboxysulpho naphthalimide or CSN) will change more than 10% if the compound encounters more than 3100 ppm of silicates (as SiO2), or if it encounters more than 41000 ppm of sodium (as Na+).
The instant claimed compounds have been found to remain inert when encountering the standard components of industrial water systems. However, it has also been found that the inertness of the instant claimed compounds can be challenged by a change in pH. The DSN compound has been found to be inert over a pH range of from about 2 to about 9 and the CSN compound has been found to be inert over a pH range of from about 5 to about 10. When operating the water system within these pH ranges it has been found that both DSN and CSN are effective inert fluorescent tracers.
An advantage provided by the fluorescent compounds of this invention is that they have been found to be inert to the degradation effects of oxidizing biocides. Therefore, they are particularly useful in systems using oxidizing biocide(s) to minimize microbial activity.